The present invention is related to a sheet feeder of an image forming apparatus having a roller attaching and detaching mechanism by which a roller can be easily replaced, and further the rotation of a shaft on which the roller is mounted is seldom obstructed by the mechanism.
In an image forming apparatus such as an electrophotographic copier and a laser beam printer, there are provided a plurality of sheet feeding trays in the sheet feeding section, and sheets of paper of different sizes are accommodated on the sheet feeding trays, so that sheets of paper of various sizes can be fed and images of various enlargement and reduction ratios can be formed on sheets of paper. Corresponding to the sheet feeding trays arranged in the sheet feeding section of the image forming apparatus, there is provided a sheet feeder in the sheet feeding section of the image forming apparatus. In accordance with an output of information about the selection of sheets of paper outputted by a control unit of the image forming apparatus, a sheet feeder corresponding to the command is operated, and sheets of paper are fed while they are handled one by one.
For example, a conventional sheet feeder arranged in the sheet feed section of the image forming apparatus is disclosed in Japanese Unexamined Patent Publication No. Hei. 2-231,324. The above conventional example is shown in FIG. 14. As shown in the drawing, there is provided a sheet feeding unit 10 in the sheet feeding section of the image forming apparatus, which composes a means for feeding sheets of paper from a sheet feeding tray 1. In the example shown in FIG. 14, there is provided a bottom plate 2 for supporting sheets of paper on the sheet feed tray 1, and also there is provided a restriction guide 3 at a rear end of the tray with respect to the sheet feeding direction. In order to attach the sheet feeding tray 1 to the sheet feeing section and also to detach the sheet feeding tray 1 from the sheet feeing section, there are provided guide rails 4, 4a so that the sheet feeding tray can be easily moved. The bottom plate 2 arranged on the sheet feeding side of sheets of paper is moved upward and downward by a lifting arm 5. The bottom plate 2 is oscillated to a position at which the sheet of paper P comes into contact with a pickup roller 85, which is arranged in the sheet feeding unit, with a predetermined pressure, so that the sheet feeding motion can be easily conducted.
The sheet feeding unit includes: a pickup roller 85 to pick up sheets of paper accommodated in the sheet feeding tray; a sheet feeding roller 61 which composes a sheet handling device; a retard roller 30; and a conveyance roller device 17 arranged at a position which corresponds to an end of the sheet feeding path 16. An end of the sheet feeding unit composes a portion of the sheet conveyance path 15 arranged upward and downward along the side of the sheet feeding section. The end of the sheet feeding unit conveys a sheet of paper upward which is sent from the sheet feeding unit arranged in the lower portion. A roller unit arranged in the above sheet feeding unit is composed as shown in FIG. 15. The retard roller 30 composing a sheet handling device is supported at a position under the sheet feeding roller 61 by a bracket 31 capable of oscillating around a support shaft 32. The retard roller 30 is pushed toward the sheet feeding roller by the action of an elastic member 33. There is provided a torque limiter 34 in the drive system to drive the retard roller 30. In order to drive the retard roller 30 in the same direction as the rotational direction of the sheet feeding roller 61, there is provided a drive unit 23, so that a handling action can be conducted on a sheet of paper between the sheet feeding roller 61 and the retard roller 30.
The sheet feeding roller 61 arranged above the retard roller 30 is combined with the pickup roller 85, so that a sheet feeding roller unit 50 can be composed. The sheet feeding roller 61 and the pickup roller 85 are supported by one support bracket 51. The pickup roller 85 is arranged in such a manner that the pickup roller 85 can be oscillated around a sheet feeding roller shaft 60 of the sheet feeding roller 61. When the pickup roller 85 is lowered, it comes into contact with an upper surface of the uppermost sheet of paper accommodated on the sheet feeding tray. An arm 55a is protruded from the side of a support bracket 51 of the sheet feeding roller unit. The arm 55a is engaged with an arm 37 of a link 36 oscillated by a solenoid 35, so that the sheet feeding roller unit 50 can be moved upward and downward by the action of the solenoid 35. Due to this operation, sheets of paper can be fed from the sheet feeding tray. In addition to the above arrangement, the following arrangement is provided. Under the condition that the pickup roller is lowered and set at a position on the sheet of paper P accommodated on the sheet feeding tray, a piece of information about the height of the stack of sheets of paper is obtained by a detection means of the sheet height sensor 57. According to the thus obtained information, the bottom plate lifting mechanism shown in FIG. 14 is operated, so that the position at which the upper surface of sheets of paper comes into contact with the pickup roller can be regulated.
In the sheet feeder composed in the manner described above, roller members such as a sheet feeding roller and a retard roller are made of rubber. Accordingly, the roller members tend to be stained and worn out by abrasion. As a result, the sheet feeding characteristics of the rollers are deteriorated, and sheets of paper can not be fed smoothly. In this case, it is necessary to replace the defective rollers. In order to solve the above problems, in the conventional sheet feeder, the roller and support shaft are integrated into one body, and in the case of abrasion of the roller, both the roller and the support shaft are replaced all together. In the case of the sheet feeding unit shown in FIG. 15, the sheet feeding roller unit can be integrally replaced with respect to the sheet feeding unit.
In this case, the following problems may be encountered. When the sheet feeding roller unit is integrally replaced with respect to the sheet feeding unit, it is complicated to attach the roller shafts to the frame of the sheet feeder, and it is also complicated to detach the roller shafts from the frame of the sheet feeder. For example, when the shafts are attached to or detached from the frame of the sheet feeder, it is necessary to attach and detach a number of small fixing members such as E-rings, screws and others, and it is very complicated to control such small parts. Accordingly, even when repair parts are distributed to a user so that they can be replaced by the user in the process of maintenance, the user can not maintain the apparatus by himself. Therefore, a skilled service man must visit the user and replace the sheet feeding roller unit.